Yang, H. and Xiao, F. (2014) Instability analyses of a top-tensioned riser under combined vortex and multi-frequency parametric excitations. Ocean Engineering, 81, pp. 12-28. (doi: 10.1016/j.oceaneng.2014.02.006)
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Abstract
This study investigates the non-linear dynamic responses of a top-tensioned riser (TTR) under combined parametric and external vortex excitations. In real sea conditions, risers simultaneously encounter waves and flow. A general analysis considers only parametric excitation resulting from platform motions or vortex-shedding excitation due to flow bypassing the risers. However, the instability of a TTR under combined excitations can lead to fatigue damage; therefore it is essential to explore the dynamic characteristics in order to maintain the safety and avoid accidents. A derived TTR model subjected to multi-frequency parametric and vortex shedding excitation has been proposed, and different cases of excitation combinations were compared. The effects of key design parameters on the dynamic properties of a TTR under combined excitation are discussed. The surface distribution of instability for a TTR system under multi-frequency parametric and vortex-shedding excitations was analyzed on the basis of various significant wave height and wave peak period combinations, and extreme sea states were considered to determine the maximum strength of a TTR. Several interesting phenomena were observed. The instability of a TTR system excited by combined excitation could be more unstable than that excited only by parametric excitation or vortex-shedding excitation. It can be concluded that the effect of vortex shedding is predominant in the excited instability of a TTR under combined excitation when the outside sea state is mild, but when the sea states is severe, parametric excitation contributes more to the instability, vortex-shedding excitation only strengthens the consequent instability. More modes and a higher frequency of vibration can be excited when extreme states are more severe.
Item Type: | Articles |
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Status: | Published |
Refereed: | Yes |
Glasgow Author(s) Enlighten ID: | Yang, Dr Hezhen |
Authors: | Yang, H., and Xiao, F. |
College/School: | College of Science and Engineering > School of Engineering > Infrastructure and Environment |
Journal Name: | Ocean Engineering |
Publisher: | Elsevier |
ISSN: | 0029-8018 |
ISSN (Online): | 1873-5258 |
Published Online: | 05 March 2014 |
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